Communication device, communication system, connection destination control method, and transmission rate control method

ABSTRACT

A communication device includes a wireless communication device, a location information acquisition device, a storage and a controller. The wireless communication device wirelessly communicates with a base station used as a connection destination. The location information acquisition device acquires location information on a location of the communication device. The storage stores historical communication information on past communication status. The controller determines a degree of risk of occurrence of reduction in an amount of available communication bandwidth beyond a tolerance limit based on the historical communication information and the location information. The controller further controls a transmission rate for communicating the data based on a result of determination of the degree of risk.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.16/631,730, filed on Jan. 16, 2020, which is a U.S. National Phase under35 U.S.C. § 371 of International Application No. PCT/JP2018/021763,filed on Jun. 6, 2018, which in turn claims the benefit of JapaneseApplication No. 2017-139202, filed on Jul. 18, 2017. The disclosure ofeach of these documents, including the specification, drawings, andclaims, is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a communication device forcommunicating data via a base station used as a connection destination,a communication system in which a communication device communicates datavia a base station used as a connection destination, a connectiondestination control method for controlling a connection destination fora communication device to communicate data via a base station used asthe connection destination, and a transmission rate control method forcontrolling a transmission rate at which a communication devicecommunicates data via a base station used as a connection destination.

BACKGROUND ART

Presently, 5G systems (Fifth generation mobile communication systems)are being considered for introduction into general use in wirelesscommunications. 5G wireless communication systems enable communicationsat high transmission capacities of more than 10 Gbps by utilizing highfrequency bands such as high SHF band and EHF band. Such high frequencybands have not been used for mobile radio communications so far and thusallow wider available communication bandwidths to be secured for use incommunications. Such communication schemes utilizing high frequencybands can provide communications at high transmission capacities, butinvolve a problem of decrease in communication quality when an obstacleis located on a communication path, which problem is caused due to thefact that higher-frequency electromagnetic waves tend to travel instraight lines.

Meanwhile, in recent years, because of increasing amounts of video datashot by mobile devices (such as smartphone and tablet) and uploaded toservers or those downloaded from servers to such mobile devices forviewing, what is called “mobile video traffic” for transmitting largeamounts of video data through mobile communications is expanding.Accordingly, there is an increasing need for 5G systems using highfrequency bands and supporting high capacity communications which areexpected to be capable of accommodating such large amounts of videodata.

However, when using high capacity communications at high frequencybands, users are likely to encounter significant reduction in QoE(Quality of Experience) because, as described above, decrease incommunication quality by obstruction is likely to occur, which can causea choppy picture when communicating video data in the form of a realtime video stream or in other forms for displaying and viewing.

Thus, one possible solution is to perform communication in such a manneras to avoid an obstructed area(s) where decrease in communicationquality occurs due to obstruction. Known technical ideas related to theavoidance of a specific area(s) include one in which a communicationdevice is configured to have a pre-defined obstructed area(s) in whicheach communication device is disabled to perform wireless communicationat a corresponding specific frequency, and when the device enters itsobstructed area, the device changes the frequency used for communicationto a different one as appropriate. (See Patent Document 1)

PRIOR ART DOCUMENT(S) Patent Document(S)

-   Patent Document 1: WO2014/102891A

SUMMARY OF THE INVENTION Task to be Accomplished by the Invention

As the above-described technology of the prior art, a communicationdevice configured to perform wireless communication in such a manner asto avoid a specific area(s); that is, an obstructed area(s) in whichdecrease in communication quality occurs by obstruction, canprospectively avoid decrease in communication quality, therebypreventing significant reduction in QoE due to a choppy picture of theviewed streaming video. However, there are various types of obstaclessuch as road signs, traffic lights, trees, and signboards and the stateof each obstacle can change with time. Thus, to precisely pre-define anobstructed area(s) is of great difficulty in reality. Accordingly, theproblem of inability to prospectively avoid decrease in communicationquality by obstruction remains unresolved.

Moreover, the amount of available communication bandwidth cansignificantly vary depending on different connection destinations. Thus,when a change in the connection destination causes rapid decrease in theamount of available communication bandwidth, significant reduction inQoE is likely to occur due to a choppy picture in a similar manner tothat of the above-described technology. Thus, them is also need fortechnology to prospectively avoid rapid reduction in the amount ofavailable communication bandwidth.

The present invention has been made in view of the problem of the priorart, and a primary object of the present invention is to provide acommunication device, a communication system, a connection destinationcontrol method, and a transmission rate control method which allow forprospective avoidance of decrease in communication quality due toobstruction and/or rapid reduction in an amount of availablecommunication bandwidth, thereby enabling users to avoid experiencingsignificant reduction in QoE.

Means to Accomplish the Task

An aspect of the present invention provides a communication device forcommunicating data via a base station used as a connection destination,the communication device comprising: a wireless communication deviceconfigured to wirelessly communicate with the base station used as theconnection destination; a location information acquisition deviceconfigured to acquire location information on a location of thecommunication device; a storage configured to store historicalobstruction information for an obstructed location where decrease incommunication quality due to obstruction has occurred before; acontroller configured to: determine a degree of risk of occurrence ofdecrease in communication quality due to obstruction based on thehistorical obstruction information and the location information, thedegree of risk being determined for at least one of a current connectiondestination that is currently used by the communication device and afuture connection destination that is expected to be used by thecommunication device; and control the connection destination based on aresult of determination of the degree of risk.

Another aspect of the present invention provides a communication devicefor communicating data via a base station used as a connectiondestination, the communication device comprising: a wirelesscommunication device configured to wirelessly communicate with the basestation used as the connection destination; a location informationacquisition device configured to acquire location information on alocation of the communication device; a storage configured to storehistorical communication information on past communication status; and acontroller configured to: determine a degree of risk of occurrence ofreduction in an amount of available communication bandwidth beyond atolerance limit based on the historical communication information andthe location information, the degree of risk being determined for anexpected location at which the communication device is expected to belocated after a lapse of a predetermined time period; and control atransmission rate for communicating the data based on a result ofdetermination of the degree of risk.

Yet another aspect of the present invention provides a communicationsystem in which a communication device communicates data via a basestation used as a connection destination, wherein the communicationdevice comprises: a wireless communication device configured towirelessly communicate with the base station used as the connectiondestination; a location information acquisition device configured toacquire location information on a location of the communication device;a storage configured to store historical obstruction information for anobstructed location where decrease in communication quality due toobstruction has occurred before; a controller configured to: determine adegree of risk of occurrence of decrease in communication quality due toobstruction based on the historical obstruction information and thelocation information, the degree of risk being determined for at leastone of a current connection destination that is currently used by thecommunication device and a future connection destination that isexpected to be used by the communication device; and control theconnection destination based on a result of determination of the degreeof risk.

Yet another aspect of the present invention provides a communicationsystem in which a communication device communicates data via a basestation used as a connection destination, wherein the communicationdevice comprises: a wireless communication device configured towirelessly communicate with the base station used as the connectiondestination; a location information acquisition device configured toacquire location information on a location of the communication device;a storage configured to store historical communication information onpast communication status; and a controller configured to: determine adegree of risk of occurrence of reduction in an amount of availablecommunication bandwidth beyond a tolerance limit based on the historicalcommunication information and the location information, the degree ofrisk being determined for an expected location at which thecommunication device is expected to be located after a lapse of apredetermined time period; and control a transmission rate forcommunicating the data based on a result of determination of the degreeof risk.

Yet another aspect of the present invention provides a connectiondestination control method for controlling a connection destination fora communication device to communicate data via a base station used asthe connection destination, the method comprising: the communicationdevice determining a degree of risk of occurrence of decrease incommunication quality due to obstruction based on historical obstructioninformation and location information on a location of the communicationdevice, the historical obstruction information being information on oneor more obstructed locations where decrease in communication quality dueto obstruction has occurred before, and the degree of risk beingdetermined for at least one of a current connection destination that iscurrently used by the communication device and a future connectiondestination that is expected to be used by the communication device; andthe communication device controlling the connection destination based ona result of determination of the degree of risk.

Yet another aspect of the present invention provides a transmission ratecontrol method for controlling a transmission rate at which acommunication device communicates data via a base station used as aconnection destination, the method comprising: the communication devicedetermine a degree of risk of occurrence of reduction in an amount ofavailable communication bandwidth beyond a tolerance limit based onhistorical communication information on past communication status andlocation information on a location of the communication device, thedegree of risk being determined for an expected location at which thecommunication device is expected to be located after a lapse of apredetermined time period; and the communication device controlling atransmission rate for communicating the data based on a result ofdetermination of the degree of risk.

Effect of the Invention

According to the present invention, when there is a risk of occurrenceof decrease in communication quality due to obstruction, a connectiondestination is prospectively changed to a different safer connectiondestination. As a result, a communication device can prospectively avoiddecrease in communication quality due to obstruction, thereby enablingusers to avoid experiencing significant reduction in QoE. Moreover, whenthere is a risk of occurrence of rapid reduction in an amount ofavailable communication bandwidth beyond a tolerance limit, atransmission rate is prospectively changed to a safer transmission rate.As a result, a communication device can prospectively avoid rapidreduction in an amount of available communication bandwidth, therebyenabling users to avoid experiencing significant reduction in QoE.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a general configuration of a communicationsystem according to a first embodiment of the present invention:

FIGS. 2A and 2B are explanatory views showing an outline of connectiondestination (CD) control operations performed by a user terminal 1according to the first embodiment of the present invention;

FIG. 3 is a block diagram showing a general configuration of a macrocell base station 3 according to the first embodiment of the presentinvention:

FIG. 4 is a block diagram showing a general configuration of a userterminal 1 according to the first embodiment of the present invention;

FIG. 5 is an explanatory view showing an example of historicalobstruction information registered in a communication history databaseaccording to the first embodiment of the present invention;

FIG. 6 is a flowchart showing an operation procedure of registration anddeletion of historical obstruction information performed by the userterminal 1 according to the first embodiment of the present invention:

FIG. 7 is a sequence diagram showing an operation procedure ofregistration and deletion of historical obstruction informationperformed by the user terminal 1 according to the first embodiment ofthe present invention;

FIGS. 8A, 8B, and 8C are explanatory views showing a risky area definedby a connection destination controller 56 according to the firstembodiment of the present invention:

FIG. 9 is a flowchart showing an operation procedure of a connectiondestination change operation performed by the user terminal 1 accordingto the first embodiment of the present invention;

FIG. 10 is a flowchart showing an operation procedure of a connectiondestination candidate selection operation performed by the user terminal1 according to the first embodiment of the present invention;

FIG. 11 is a sequence diagram showing an operation procedure of the userterminal 1 according to the first embodiment of the present invention;

FIG. 12 is a flowchart showing an operation procedure of a connectiondestination change operation performed by a user terminal 1 according toa second embodiment of the present invention;

FIG. 13 is a flowchart showing an operation procedure of a connectiondestination candidate selection operation performed by the user terminal1 according to the second embodiment of the present invention;

FIGS. 14A and 14B are explanatory views showing an outline of connectiondestination control operations performed by a user terminal 1 accordingto a third embodiment of the present invention;

FIG. 15 is a block diagram showing a general configuration of a userterminal 1 according to a fourth embodiment of the present invention;

FIG. 16 is an explanatory view showing an example of historicalcommunication information registered in a communication history databaseaccording to the fourth embodiment of the present invention;

FIG. 17 is a flowchart showing an operation procedure of the userterminal 1 according to the fourth embodiment of the present invention;

FIG. 18 is a sequence diagram showing an operation procedure of the userterminal 1 according to the fourth embodiment of the present invention;

FIG. 19 is an explanatory view showing an example of a transmission ratetable according to a fifth embodiment of the present invention; and

FIG. 20 is a flowchart showing an operation procedure of a user terminal1 according to the fifth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A first aspect of the present invention made to achieve theabove-described object is a communication device for communicating datavia a base station used as a connection destination, the communicationdevice comprising: a wireless communication device configured towirelessly communicate with the base station used as the connectiondestination; a location information acquisition device configured toacquire location information on a location of the communication device;a storage configured to store historical obstruction information for anobstructed location where decrease in communication quality due toobstruction has occurred before; a controller configured to: determine adegree of risk of occurrence of decrease in communication quality due toobstruction based on the historical obstruction information and thelocation information, the degree of risk being determined for at leastone of a current connection destination that is currently used by thecommunication device and a future connection destination that isexpected to be used by the communication device; and control theconnection destination based on a result of determination of the degreeof risk.

In this configuration, when there is a risk of occurrence of decrease incommunication quality due to obstruction, a connection destination isprospectively changed to a different safer connection destination. As aresult, a communication device can prospectively avoid decrease incommunication quality due to obstruction, thereby enabling users toavoid experiencing significant reduction in QoE.

A second aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured to control a cellof the connection destination.

In this configuration, when decrease in communication quality due toobstruction occurs in a specific cell, a connection destination can bechanged to a safer cell so as to avoid the specific cell.

A third aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured to control a beamof the connection destination.

In this configuration, when decrease in communication quality due toobstruction occurs in a specific beam, a connection destination can bechanged to a safer beam so as to avoid the specific beam.

A fourth aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured such that, whenthere is a risk of occurrence of decrease in communication quality dueto obstruction associated with the current connection destination, thecontroller changes the connection destination from the currentconnection destination to a different connection destination.

In this configuration, since a connection destination is changed fromone which involves a risk of occurrence of decrease in communicationquality due to obstruction to a safe connection destination, acommunication device can prospectively avoid decrease in communicationquality due to obstruction.

A fifth aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured such that, whenthere is a risk of occurrence of decrease in communication quality dueto obstruction associated with the future connection destination as aconnection destination candidate, the controller control the connectiondestination in such a manner as to avoid selecting the future connectiondestination as a connection destination.

In this configuration, since, upon a change in a connection destination(handover), a safe connection destination in which decrease incommunication quality due to obstruction does not occur is selected as anew connection destination, a communication device can prospectivelyavoid decrease in communication quality due to obstruction.

A sixth aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured to define a riskyarea around the obstructed location, and to determine the degree of riskbased on whether or not the communication device is present in the riskyarea.

In this configuration, prior to actual occurrence of decrease incommunication quality due to obstruction, a degree of risk of occurrenceof decrease in communication quality can be precisely determined.

A seventh aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured to determine thedegree of risk based on an accession time required for the communicationdevice to reach the obstructed location.

In this configuration, prior to actual occurrence of decrease incommunication quality due to obstruction, a degree of risk of occurrenceof decrease in communication quality can be precisely determined.

An eighth aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured to determine thedegree of risk based on moving status of the communication device.

In this configuration, a degree of risk of occurrence of decrease incommunication quality can be precisely determined by taking movingstatus of a communication device into consideration.

A ninth aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured to determine thedegree of risk based on a type of application currently performingcommunication.

In this configuration, a degree of risk of occurrence of decrease incommunication quality can be properly determined so as to meettransmission characteristics required by a type of application currentlyperforming communication.

A tenth aspect of the present invention is the communication device ofthe first aspect, wherein the controller is configured to determine thedegree of risk based on a type of the communication device.

In this configuration, a degree of risk of occurrence of decrease incommunication quality can be properly determined so as to meettransmission characteristics required by a type of communication device.

An eleventh aspect of the present invention is a communication devicefor communicating data via a base station used as a connectiondestination, the communication device comprising: a wirelesscommunication device configured to wirelessly communicate with the basestation used as the connection destination; a location informationacquisition device configured to acquire location information on alocation of the communication device; a storage configured to storehistorical communication information on past communication status; and acontroller configured to: determine a degree of risk of occurrence ofreduction in an amount of available communication bandwidth beyond atolerance limit based on the historical communication information andthe location information, the degree of risk being determined for anexpected location at which the communication device is expected to belocated after a lapse of a predetermined time period; and control atransmission rate for communicating the data based on a result ofdetermination of the degree of risk.

In this configuration, when there is a risk of occurrence of rapidreduction in an amount of available communication bandwidth beyond atolerance limit, a transmission rate is prospectively changed to a safertransmission rate. As a result, a communication device can prospectivelyavoid rapid reduction in an amount of available communication bandwidth,thereby enabling users to avoid experiencing significant reduction inQoE.

A twelfth aspect of the present invention is the communication device ofthe eleventh aspect, wherein the storage configured to store atransmission rate and application information both for each location ashistorical communication information, and

wherein the controller is configured to, based on the historicalcommunication information, acquire application information on anapplication currently performing communication and an expectedtransmission rate at the expected location, and communicates the data atthe expected transmission rate.

This configuration enables a communication device to communicate data ata proper transmission rate.

A thirteenth aspect of the present invention is the communication deviceof the twelfth aspect, wherein the controller is configured to determinethat there is a risk of occurrence of decrease in communication qualitydue to obstruction when the expected transmission rate is lower than acurrent transmission rate by a rate difference which is greater than apredetermined threshold value.

This configuration enables a communication device to precisely determinea degree of risk of occurrence of rapid reduction in an amount ofavailable communication bandwidth beyond a tolerance limit.

A fourteenth aspect of the present invention is the communication deviceof the eleventh aspect, wherein the storage configured to store aconnection destination for each location as historical communicationinformation, and

wherein the controller is configured to, based on the historicalcommunication information, acquire an expected connection destination atthe expected location, and communicate the data at a transmission ratefor the expected connection destination.

This configuration enables a communication device to communicate data ata proper transmission rate.

A fifteenth aspect of the present invention is the communication deviceof the fourteenth aspect, wherein the controller is configured todetermine that there is a risk of occurrence of decrease incommunication quality due to obstruction when a transmission capacity ofthe expected connection destination at the expected location is lowerthan that of a current connection destination.

This configuration enables a communication device to precisely determinea degree of risk of occurrence of rapid reduction in an amount ofavailable communication bandwidth beyond a tolerance limit.

A sixteenth aspect of the present invention is a communication system inwhich a communication device communicates data via a base station usedas a connection destination, wherein the communication device comprises:a wireless communication device configured to wirelessly communicatewith the base station used as the connection destination; a locationinformation acquisition device configured to acquire locationinformation on a location of the communication device; a storageconfigured to store historical obstruction information for an obstructedlocation where decrease in communication quality due to obstruction hasoccurred before; a controller configured to: determine a degree of riskof occurrence of decrease in communication quality due to obstructionbased on the historical obstruction information and the locationinformation, the degree of risk being determined for at least one of acurrent connection destination that is currently used by thecommunication device and a future connection destination that isexpected to be used by the communication device; and control theconnection destination based on a result of determination of the degreeof risk.

This configuration enables a communication device to prospectively avoiddecrease in communication quality due to obstruction, thereby enablingusers to avoid experiencing significant reduction in QoE in the samemanner as the first aspect of the present invention.

A seventeenth aspect of the present invention is a communication systemin which a communication device communicates data via a base stationused as a connection destination, wherein the communication devicecomprises: a wireless communication device configured to wirelesslycommunicate with the base station used as the connection destination; alocation information acquisition device configured to acquire locationinformation on a location of the communication device; a storageconfigured to store historical communication information on pastcommunication status; and a controller configured to: determine a degreeof risk of occurrence of reduction in an amount of availablecommunication bandwidth beyond a tolerance limit based on the historicalcommunication information and the location information, the degree ofrisk being determined for an expected location at which thecommunication device is expected to be located after a lapse of apredetermined time period; and control a transmission rate forcommunicating the data based on a result of determination of the degreeof risk.

This configuration enables a communication device to prospectively avoidrapid reduction in an amount of available communication bandwidth,thereby enabling users to avoid experiencing significant reduction inQoE in the same manner as the eleventh aspect of the present invention.

An eighteenth aspect of the present invention is a connectiondestination control method for controlling a connection destination fora communication device to communicate data via a base station used asthe connection destination, the method comprising: the communicationdevice determining a degree of risk of occurrence of decrease incommunication quality due to obstruction based on historical obstructioninformation and location information on a location of the communicationdevice, the historical obstruction information being information on oneor more obstructed locations where decrease in communication quality dueto obstruction has occurred before, and the degree of risk beingdetermined for at least one of a current connection destination that iscurrently used by the communication device and a future connectiondestination that is expected to be used by the communication device; andthe communication device controlling the connection destination based ona result of determination of the degree of risk.

This configuration enables a communication device to prospectively avoiddecrease in communication quality due to obstruction, thereby enablingusers to avoid experiencing significant reduction in QoE in the samemanner as the first aspect of the present invention.

A nineteenth aspect of the present invention is a transmission ratecontrol method for controlling a transmission rate at which acommunication device communicates data via a base station used as aconnection destination, the method comprising: the communication devicedetermine a degree of risk of occurrence of reduction in an amount ofavailable communication bandwidth beyond a tolerance limit based onhistorical communication information on past communication status andlocation information on a location of the communication device, thedegree of risk being determined for an expected location at which thecommunication device is expected to be located after a lapse of apredetermined time period; and the communication device controlling atransmission rate for communicating the data based on a result ofdetermination of the degree of risk.

This configuration enables a communication device to prospectively avoidrapid reduction in an amount of available communication bandwidth,thereby enabling users to avoid experiencing significant reduction inQoE in the same manner as the eleventh aspect of the present invention.

Embodiments of the present invention will be described below withreference to the drawings.

First Embodiment

FIG. 1 is a diagram showing a general configuration of a communicationsystem according to a first embodiment of the present invention.

The communication system includes a user terminal 1 (communicationdevice), a server 2, a macro cell base station 3 (base station device),small cell base stations 4 (base station devices), a wireless LAN basestation 5 (access point, base station), and a communication controldevice 6.

A communication area of the macro cell base station 3 overlaps withthose of the small cell base stations 4 and the wireless LAN basestation, whereby what is called a heterogeneous network is constructed,in which a communication environment supporting multiple RATs (RadioAccess Technologies) is provided.

The user terminal 1 may be a smartphone, a tablet terminal, and anyother suitable terminal device. The user terminal 1 is capable of beingconnected to the base stations 3, 4 and 5, which construct theheterogeneous network. The user terminal 1 communicates with the server2 via the heterogeneous network, a wired network including the Internetand a core-network.

The server 2 is configured to communicate with the user terminal 1 inorder to receive and transmit various data which the user terminal 1uploads to and downloads from the server 2. For example, the server 2receives and stores video data shot by the user terminal 1, and alsodistributes various contents to the user terminal 1.

The macro cell base station 3 performs wireless communication using aUHF band, e.g. wireless communication using LTE (Long Term Evolution)scheme. The macro cell base station 3 is a C-plane cell, which handlescontrol plane (C-Plane) massages for transmitting control signals. Inother embodiments, the macro cell base station 3 may be used as aU-Plane cell, which handles user plane (U-Plane) messages fortransmitting user data.

The small cell base stations 4 perform wireless communication using ahigh SHF band or EHF band (millimeter wave band), which can comply with5G NR (New Radio). The small cell base stations 4 are used as cellshandling user plane (U-Plane) messages for transmitting user data.

The wireless LAN access point 5 is configured to perform relativelylarge capacity wireless communication using a suitable wirelesscommunication scheme such as a WiFi (Registered Trademark) communicationsystem or a WiGig (Registered Trademark) communication system.

The communication control device 6 may be an LTE communication devicesuch as S-GW (Serving Gateway) or P-GW (Packet data network Gateway) forcontrolling wireless communication using a macro cell base station(LTE), or an NR communication device such as SMF (Session ManagementFunction) device or UPF (User Plane Function) device for controllingwireless communication using a small cell base station (NR).

Next, connection destination (CD) control operations performed by a userterminal 1 according to the first embodiment of the present inventionwill be described. FIG. 2 is an explanatory view showing an outline ofconnection destination control operations performed by the user terminal1.

In cases where an obstacle(s) such as a building exists within a cell, aspace hidden behind the obstacle as seen from a base station 3, 4, 5includes an obstructed area formed therein where decrease incommunication quality can occur due to blockage of radius waves by theobstacle. When the user terminal 1 enters the obstructed area, decreasein communication quality can occur due to obstruction, which can cause achoppy picture when displaying and viewing a video stream, resulting insignificant reduction in QoE (Quality of Experience).

Meanwhile, there are various types of obstacles other than buildingssuch as road signs, traffic lights, trees, and signboards. In addition,the state of each obstacle can change with time (e.g. tree felling,removal of signboard, and sparse traffic). Thus, to precisely define anobstructed area(s) based on the state of an obstacle is of greatdifficulty.

In order to address the above problem, in the present embodiment, acommunication device such as the user terminal 1 accumulates historicalobstruction information for an obstructed location where decrease incommunication quality due to obstruction has occurred before;determining whether or not the user terminal 1 has reached a locationclose to the obstructed location based on the historical obstructioninformation and location information on a location of the user terminal1; determines a degree of risk of occurrence of decrease incommunication quality due to obstruction based on a result of thelocation-related determination; and control a connection destinationbased on a result of determination of the degree of risk so as not toselect a cell corresponding to the obstructed location.

In the present embodiment, the user terminal 1 performs differentconnection destination control operations depending on which of thefollowing two cases: one is a case where, as shown in FIG. 2A, the userterminal 1 has not reached a boundary of a currently-connected cell andthe other is a case where, as shown in FIG. 2B, the user terminal 1 hasreached a boundary of a currently-connected cell (the left cell in FIG.2B).

In the case where the user terminal 1 has not reached a boundary of acurrently-connected cell as shown in FIG. 2A, control operations areperformed such that the user terminal determines a degree of risk ofoccurrence of decrease in communication quality associated with acurrent connection destination (a connection destination currently usedby the user terminal) and changes its connection destination asnecessary.

Specifically, when the user terminal 1 reaches a location close to theobstructed location, the user terminal temporarily changes itsconnection destination to a different cell (an alternative cell) fromthe currently-connected cell. For example, in cases where thecurrently-connected cell is a small cell providing a large amount ofavailable communication bandwidth, when the user terminal 1 reaches alocation close to the obstructed location associated with the small cellproviding the large amount of available communication bandwidth, theuser terminal temporarily changes its connection destination to themacro cell providing a small amount of available communication bandwidthas an alternative cell. In this case, if the user terminal 1 then movesaway from the obstructed location, the user terminal changes itsconnection destination back to the small cell.

In the case where the user terminal 1 has reached a boundary of acurrently-connected cell as shown in FIG. 2B, control operations amperformed such that the user terminal determines one or more degrees ofrisk of occurrence of decrease in communication quality associated withone or more nearby connection destinations; that is, one or moreconnection destination candidates (adjacent cells) in order to select afuture connection destination from the candidates to thereby carry out achange in its connection destination (handover) as appropriate.

Specifically, when the user terminal 1 reaches a location close to anobstructed location associated with one of the connection destinationcandidates, the user terminal controls its connection destination so asto exclude a cell corresponding to the obstructed location fromconnection destination candidates. For example, even in cases whereconnection destination candidates include a small cell providing a largeamount of available communication bandwidth, when the user terminal 1reaches a location close to an obstructed location associated with thesmall cell, the user terminal excludes the small cell from theconnection destination candidates and selects the macro cell providing asmall amount of available communication bandwidth as an alternativecell.

Connection destination candidates are cells which are connectable to theuser terminal 1 (i.e. the macro cell, the small cell(s), and thewireless LAN cell), and are reported from the macro cell base station 3or any other source. In other embodiments, the user terminal 1 may beconfigured to search connectable cells by itself to acquire informationon connection destination candidates.

Next, a general configuration of the macro cell base station 3 accordingto the first embodiment of the present invention will be described. FIG.3 is a block diagram showing a general configuration of the macro cellbase station 3.

The macro cell base station 3 includes a wireless communication device11, a wired communication device 12, a controller 13, and a storage 14.

The wireless communication device 11 performs wireless communicationwith the user terminal 1.

The wired communication device 12 performs wired communication with thecommunication control device 6 such as S-GW, a nearby macro cell basestation(s) 3 and/or a nearby small cell base station(s) 4.

The storage 14 stores information on the user terminal 1, information onother nearby macro cell base station(s) 3 and small cell base station(s)4, and a program(s) executable by a processor which implements thecontroller 13.

The controller 13 includes a wireless communication controller 21 and awired communication controller 22. The controller 13 is implemented bythe processor, and each part of the controller 13 is implemented by theprocessor executing a corresponding program stored in the storage 14.

The wireless communication controller 21 is configured to controlwireless communication with the user terminal 1 based on communicationquality information transmitted from the user terminal 1, and instructthe user terminal 1 to change its connection destination to a properone.

The wired communication controller 22 is configured to exchangeinformation on connection destination(s) of the user terminal or someother information through wired communication with the communicationcontrol device 6 such as S-GW, the nearby macro cell base station(s) 3and/or the nearby small cell base station(s) 4.

In FIG. 3, the general configuration of the macro cell base station 3 isshown. However, each small cell base station 4 and the wireless LANaccess point 5 have substantially the same general configuration as themacro cell base station.

Next, a general configuration of the user terminal 1 according to thefirst embodiment of the present invention will be described. FIG. 4 is ablock diagram showing a general configuration of the user terminal 1.

The user terminal 1 includes a wireless communication device 31, alocation information acquisition device 32, a controller 33, and astorage 34.

The wireless communication device 31 performs wireless communicationwith the macro cell base station 3, the small cell base stations 4, andthe wireless LAN access point 5, which construct a 5G heterogeneousnetwork, and performs communication with the server 2 via the 5Gheterogeneous network and the wired network.

The location information acquisition device 32 acquires locationinformation on the location of the user terminal itself by using asatellite positioning system such as a GPS (Global Positioning System).

The storage 34 stores information on the user terminal itself,information on base stations 3, 4, 5. Moreover, the storage 34 storesinformation registered in a communication history database (See FIG. 5).Information registered in the communication history database includesobstructed locations where, for each of the obstructed locations,decrease in communication quality due to obstruction has occurredbefore. The storage 34 also stores programs executable by a processor,which implement the controller 33.

The controller 33 includes a wireless communication controller 41, anapplication controller 42, a terminal status acquirer 43, and anapplication information acquirer 44. The controller 33 is implemented bythe processor, and each part of the controller 33 is implemented by theprocessor executing a corresponding program stored in the storage 34.

The application controller 42 performs an operation(s) required for eachapplication, and transmits and receives data to and from the server 2via the wireless communication device 31.

The terminal status acquirer 43 acquires information on a currentlocation at which the user terminal is currently located and informationon current moving status (moving velocity and moving direction) asterminal status information.

The application information acquirer 44 monitors communication performedby the application controller 42 and acquires application information ona type of application currently performing communication.

The wireless communication controller 41 controls wireless communicationperformed by the wireless communication device 31, and includes acommunication quality measurer 51, a communication failure detector 52,an obstructed state determiner 53, a historical information manager 54,a historical information acquirer 55, and a connection destinationcontroller 56.

The communication quality measurer 51 measures a current communicationquality level associated with a currently-connected cell (serving cell).

The communication failure detector 52 detects a state in which the userterminal cannot receive a signal from any of the base stations 3, 4, and5; that is, RLF (Radio Link Failure).

The obstructed state determiner 53 determines whether or not the userterminal is in an obstructed state in which decrease in communicationquality due to obstruction is occurring based on a result of measurementby the communication quality measurer 51 and a result of detection bythe communication failure detector 52.

The historical information manager 54 determines whether or not thecurrent location is an obstructed location based on a result ofdetermination by the obstructed state determiner 53. If the currentlocation is an obstructed location, the historical information manager54 registers current location information and information on currentcommunication status in the communication history database in thestorage 34 as historical obstruction information.

Preferably, the historical information manager 54 may be configured todetermine that the current location is an obstructed location when theobstructed state is detected continuously for a predetermined number oftimes. In this configuration, accidental decreases in communicationquality due to obstruction by moving obstacles can be left out ofconsideration in determining the obstructed state. In other cases wherethe obstructed state is frequently detected, the historical informationmanager 54 may be configured to determine that the current location isan obstructed location when the obstructed state is detected apredetermined number of times within a predetermined time period.

If the historical information manager 54 determines that the currentlocation is not an obstructed location based on a result ofdetermination by the obstructed state determiner 53, the historicalinformation manager 54 transmits an inquiry to the historicalinformation manager 54 to check whether or not the communication historydatabase includes historical obstruction information for the currentlocation. When the communication history database includes historicalobstruction information for the current location, the historicalinformation manager 54 determines that an obstacle associated with thecurrent location is removed and deletes the historical obstructioninformation for the current location from the communication historydatabase.

Preferably, the historical information manager 54 may be configured todetermine that the current location is a non-obstructed location whenthe obstructed state is not detected continuously for a predeterminednumber of times. In this configuration, accidental decreases incommunication quality due to obstruction by moving obstacles can be leftout of consideration in determining the obstructed state. In other caseswhere such a non-obstructed state is frequently detected, the historicalinformation manager 54 may be configured to determine that the currentlocation is a non-obstructed location when the non-obstructed state isdetected a predetermined number of times within a predetermined timeperiod.

Targets of the measurement by the communication quality measurer 51 andthe detection by the communication failure detector 52 include acurrently-connected cell, connection destination candidates (adjacentcells) reported from the macro cell base station 3, and thus thecommunication history database is updated as necessary.

In response to an inquiry transmitted from the connection destinationcontroller 56, the historical information acquirer 55 searches andacquires historical obstruction information for the current connectiondestination in the communication history database stored in the storage34. Also, in response to an inquiry transmitted from the connectiondestination controller 56, the historical information acquirer 55searches and acquires historical obstruction information for theconnection destination candidates in the communication history databasestored in the storage 34.

The connection destination controller 56 performs control operations inorder to select a proper connection destination among the macro cell andthe small cells and the cell (coverage) of the wireless LAN access pointbased on historical obstruction information acquired by the historicalinformation acquirer 55.

In the present embodiment, the user terminal determines degrees of riskof occurrence of decrease in communication quality due to obstructionassociated with a current connection destination and a future connectiondestination based on the historical obstruction information and thelocation information; and controls the connection destination based on aresult of determination of the degree of risk. In other words, the userterminal controls the connection destination such that, when there is arisk of occurrence of decrease in communication quality due toobstruction, the user terminal changes its connection destination to adifferent safer connection destination in which decrease incommunication quality due to obstruction does not occur.

Moreover, in the present embodiment, the user terminal defines a riskyarea for an obstructed location based on the status of the user terminal1, and determines in advance a degree of risk of occurrence of decreasein communication quality due to obstruction depending on whether or notthe user terminal is currently located in the risky area.

Next, a communication history database according to the first embodimentof the present invention will be described. FIG. 5 is an explanatoryview showing an example of historical obstruction information registeredin the communication history database according to the first embodimentof the present invention.

In the present embodiment, the obstructed state determiner 53 determineswhether or not the user terminal is in the obstructed state in whichdecrease in communication quality due to obstruction is occurring, andthe determination is made based on current communication qualityassociated with the currently-connected cell or any other condition, andwhen the user terminal is in the obstructed state, the informationmanager registers current location information and information oncurrent communication status in the communication history database ashistorical obstruction information.

The communication history database includes historical obstructioninformation, the historical obstruction information including anobstructed location(s); that is, a location(s) where decrease incommunication quality due to obstruction has occurred before, andcorresponding communication status. More specifically, items ofhistorical obstruction information includes date, time, location, RAT,frequency, cell ID, beam identifier, moving direction, communicationquality, rate of change in communication quality, greatest difference incommunication quality between the current location and nearby locations,and RLF determination result.

Next, an operation procedure of registration and deletion of historicalobstruction information performed by the user terminal 1 according tothe first embodiment of the present invention will be described. FIG. 6is a flowchart showing the operation procedure of the user terminal 1.FIG. 7 is a sequence diagram showing the operation procedure of the userterminal 1.

In the user terminal 1, the obstructed state determiner 53 conductsdetermination regarding current communication quality (ST101),determination regarding change in communication quality with time(ST102), determination regarding change in communication quality withlocation (ST103), and determination regarding RLF (Radio Link Failure)(ST04).

The determination regarding current communication quality (ST101) isconducted in order to determine whether or not current communicationquality is good. In this step, the obstructed state determiner 53acquires current communication quality associated with acurrently-connected cell from the communication quality measurer 51, anddetermines whether or not a value of the acquired current communicationquality is lower than a predetermined threshold value Th.

The determination regarding change in communication quality with time(ST102) is conducted in order to determine whether or not change incommunication quality with time is significant. In this step, theobstructed state determiner 53 calculates a communication qualitydecrease rate with time, and determines whether or not the calculatedcommunication quality decrease rate is greater than a predeterminedthreshold value Th.

The determination regarding change in communication quality withlocation (ST103) is conducted in order to determine whether or notchange in communication quality with location is significant. In thisstep, the obstructed state determiner 53 calculates a difference incommunication quality between the current location and a nearbylocation, and determines whether or not the calculated difference incommunication quality is greater than a predetermined threshold valueTh.

In the step of determination regarding RLF (Radio Link Failure)(ST104),the obstructed state determiner 53 acquires a result of detection of RLF(Radio Link Failure) from the communication failure detector 52, anddetermines whether RLF is detected or not.

If a value of the current communication quality is lower than apredetermined threshold value Th (Yes in ST101), or if a communicationquality decrease rate is greater than a predetermined threshold value Th(Yes in ST102), or if a difference in communication quality is greaterthan a predetermined threshold value Th (Yes in ST103), or if RLF isdetected, i.e. Radio Link Failure occurs (Yes in ST104), the obstructedstate determiner 53 determines that the current location is anobstructed location (ST105).

The historical information manager 54 acquires terminal statusinformation (current location, moving velocity and moving direction)from the terminal status acquirer 43, and the historical informationmanager 54 also acquires information on a current connection destinationfrom the connection destination controller 56 and registers currentlocation information, i.e., information on the current location(obstructed location) and information on other current communicationstatus (such as connection destination) in the communication historydatabase in the storage 34 as historical obstruction information(ST106).

If a value of the current communication quality is not lower than apredetermined threshold value Th (No in ST101), or if a communicationquality decrease rate is not greater than a predetermined thresholdvalue Th (No in ST102), or if a difference in the communication qualityis not greater than a predetermined threshold value Th (No in ST103), orif RLF is not detected (No in ST104), the obstructed state determiner 53determines that the current location is a non-obstructed location(ST107).

Then, the historical information manager 54 transmits an inquiry to thehistorical information manager 54 to check whether or not thecommunication history database includes historical obstructioninformation for the current location. If the historical obstructioninformation is present, the historical information manager 54 deletesthe historical obstruction information for the current location from thecommunication history database (ST108).

In this way, in the present embodiment, if current communication qualityis not good, or if change in communication quality with time issignificant, or if change in communication quality with location issignificant, or if RLF is detected, the obstructed state determiner 53determines that the current location is an obstructed location and thehistorical information manager 54 registers information on currentcommunication status for the current location in the communicationhistory database in the storage 34 as historical obstructioninformation.

Preferably, when performing the control operations, an area having acertain size is regarded as an obstructed location. For example, meshelement areas each having a predetermined shape (e.g. square, circle,ellipse) and a uniform size (e.g. 1 meter square) may be determined overan entire area including the macro cell, the smell cells, and thewireless LAN cell so as to enable determination of an obstructedlocation on an mesh-element-area basis.

Next, processing operations performed by the connection destinationcontroller 56 will be described. FIG. 8 is an explanatory view showing arisky area defined by the connection destination controller 56.

In the present embodiment, the connection destination controller 56defines a risky area for an obstructed location, and determines a degreeof risk of occurrence of decrease in communication quality due toobstruction based on whether or not the user terminal is currentlylocated in the risky area. A risky area is first defined in a circularshape centering on an obstructed location.

The degree of risk of occurrence of decrease in communication qualityvaries depending on whether or not the user terminal 1 reaches anobstructed location in a short time period. In this view, in the presentembodiment, the size of a risky area is determined based on movingstatus of the user terminal 1.

Whether or not the user terminal 1 reaches an obstructed location in ashort time period can be determined based on the velocity component Vain the direction A from the current location Pc to the obstructedlocation Pd of the moving velocity V of the user terminal 1. In thisview, in the present embodiment, the A-direction velocity component Vaof the moving velocity V is calculated from the current location Pc, theobstructed location Pd, and the moving velocity V and the movingdirection of the user terminal 1, and the size of a risky area isdetermined based on the A-direction velocity component Va of the movingvelocity V. Specifically, when the A-direction velocity component Va issmall, a risky area is defined to have a small size, while when theA-direction velocity component Va is large, a risky area is defined tohave a large size.

In the present embodiment, the radius of a risky area is determined byadding an offset O (correction value), which is determined by theA-direction velocity component Va of the moving velocity V, to areference radius L (e.g. 1 m).

As shown in FIG. 8A, when the moving velocity component Va is zero,(when the user terminal 1 does not move in the direction Da), the radiusof a risky area is a reference radius L determined by adding no offset Oto the reference radius L. In this case, when the distance between thecurrent location Pc of the user terminal 1 and the obstructed locationPd is smaller than the reference radius L, the user terminal 1 isdetermined to be located in a risky area and in a risky state.

As shown in FIG. 8B, when the moving velocity component Va is small,(when the user terminal 1 moves at a low velocity in the A direction),the radius of a risky area is determined by adding a small offset O tothe reference radius L. In this case, when the distance between thecurrent location Pc of the user terminal 1 and the obstructed locationPd is smaller than a value obtained by adding the small offset O to thereference radius L, the user terminal 1 is determined to be located in arisky area and in the risky state.

As shown in FIG. 8C, when the moving velocity component Va is large,(when the user terminal 1 moves at a high velocity in the A direction),the radius of a risky area is determined by adding a large offset O tothe reference radius L. In this case, when the distance between thecurrent location Pc of the user terminal 1 and the obstructed locationPd is smaller than a value obtained by adding the large offset O to thereference radius L, the user terminal 1 is determined to be located in arisky area and be in the risky state.

Required transmission characteristics such as communication stabilityvary depending on a type of application currently performingcommunication. In this view, in the present embodiment, the size of arisky area is determined based on a type of application currentlyperforming communication.

For example, in the case of an application for transferring data usingFTP, since the communication stability does not matter so much and thusmomentary interruptions and sudden drops in transmission rate arepermitted to some extent, the size of a risky area is determined to besmall, or a degree of risk of occurrence of decrease in communicationquality is determined based on whether or not the user terminal islocated in an obstructed location without using any risky area. In thecase of an application for transmitting video data, since momentaryinterruptions and sudden drops in transmission rate are not permitted,the size of a risky area is determined to be large.

How much transmission characteristics (such as communication stability)affect QoE (Quality of Experience) varies depending on a type of theuser terminal 1. In this view, in the present embodiment, the size of arisky area is determined based on a type of the user terminal 1.

For example, in the case that the user terminal 1 is one used forreporting measurement results of various meters and sensors (measuringdevices), since transmission characteristics (such as communicationstability) substantially do not affect QoE, the size of a risky area isdetermined to be small, or a degree of risk of occurrence of decrease incommunication quality is determined based on whether or not the userterminal is located in an obstructed location without using any riskyarea. In the case that the user terminal 1 is a mobile device such assmartphone, since transmission characteristics (such as communicationstability) affect QoE, the size of a risky area is determined to belarge.

In this way, in the present embodiment, the size of a risky area isdetermined based on moving status of the user terminal 1, a type ofapplication currently performing communication, and a type of the userterminal 1. However, the size of a risky area may be determined based onany one of these conditions. In other cases, the size of a risky areamay be determined based on any combination of the conditions. In thecase of determination based on any combination of these conditions,moving status of the user terminal 1 is preferably used as a primarybasis for determining a risky area.

The user terminal 1 is preferably configured to constantly measurecommunication quality levels of cells found by performing a cell searchoperation, and update communication history database as necessary basedon measurement results. In this case, when the user terminal 1 finds anew obstructed location, historical obstruction information isregistered in the communication history database, and when finding animprovement of communication quality, the user terminal 1 deleteshistorical obstruction information from the communication historydatabase.

In this case, the user terminal 1 is preferably configured such that,when the user terminal 1 finds a location where current communicationquality is good within a risky area defined in a circular shapecentering on an obstructed location, the user terminal 1 redefines therisky area by deleting such a location from the risky area. In this way,the shape of a risky area can be gradually brought closer to that of anactual obstructed area where decrease in communication quality actuallyoccurs due to obstruction, whereby a proper risky area is formed.

Next, operation procedures of a connection destination change operationand a connection destination candidate selection operation performed bythe user terminal 1 according to the first embodiment will be described.FIG. 9 is a flowchart showing an operation procedure of the connectiondestination change operation performed by the user terminal 1. FIG. 10is a flowchart showing an operation procedure of the connectiondestination candidate selection operation performed by the user terminal1. FIG. 11 is a sequence diagram showing an operation procedure of theuser terminal 1.

As shown in FIG. 9, when performing the connection destination changeoperation, the connection destination controller 56 acquires applicationinformation on an application currently performing communication fromthe application information acquirer 44, and determines whether or notthe application currently performs video communication (i.e.transmission and/or reception of video data) based on the applicationinformation (ST201).

If currently performing video communication (Yes in ST201), theconnection destination controller 56 acquires current locationinformation for a current location of the user terminal from theterminal status acquirer 43 (ST202). Also, the connection destinationcontroller 56 acquires a moving velocity and a moving direction of theuser terminal from the terminal status acquirer 43 (ST203).

Next, the connection destination controller 56 transmits an inquiry tothe historical information manager 54 to check whether or not historicalobstruction information on the current connection destination is present(ST204). Upon receiving the inquiry, the historical information manager54 searches and (if found) acquires the requested historical obstructioninformation in the communication history database stored in the storage34.

If the historical obstruction information on the current connectiondestination is present (Yes in ST204), the connection destinationcontroller 56 calculates an offset based on an obstructed locationincluded in the historical obstruction information for the currentconnection destination, a moving velocity and a moving direction of theuser terminal, and then determines an obstructed area (ST205).

Next, the connection destination controller 56 determines whether or notthe user terminal is located within a risky area based on the currentlocation information of the user terminal (ST206). Then, the connectiondestination controller 56 calculates a distance from the currentlocation of the user terminal to the obstructed location, and determineswhether the distance is greater than the radius of the risky area (avalue obtained by adding the offset to a reference value).

If the user terminal is located within the risky area (Yes in ST206),the connection destination controller 56 changes its connectiondestination (ST207).

If the connection destination controller 56 does not perform videocommunication (No in ST201), or if the user terminal is not locatedwithin the risky area (No in ST206), the connection destinationcontroller 56 ends the operation without any further processing.

It should be noted that, since a new connection destination isdetermined by a network side device such as the macro cell base station3, the connection destination controller 56 only has to request such anetwork side device to determine a new connection destination in such amanner as to avoid connecting to a particular cell(s). In this case, theconnection destination controller 56 may, for example, add informationon a cell(s)(such as cell ID) which is to be excluded from connectiondestination candidates to a cell-change request message.

In other cases, the connection destination controller 56 may transmit toa network side device a cell-change request message which requests tochange the connection destination from the current connectiondestination to a different cell. In this case, the connectiondestination controller 56 preferably adds information on a cause forrequesting the cell change (i.e. an expected communication failure dueto obstruction) to a cell-change request message.

As shown in FIG. 10, when selecting connection destination candidates,the connection destination controller 56 acquires applicationinformation on an application currently performing communication fromthe application information acquirer 44, and determines whether or notthe application currently performs video communication (i.e.,transmission and/or reception of video data) based on the applicationinformation (ST301).

If the application currently performs video communication (Yes inST301), the connection destination controller 56 acquires currentlocation information for a current location of the user terminal fromthe terminal status acquirer 43 (ST302). Also, the connectiondestination controller 56 acquires a moving velocity and a movingdirection of the user terminal from the terminal status acquirer 43(ST303).

Next, the connection destination controller 56 transmits an inquiry tothe historical information manager 54 to check whether or not historicalobstruction information on each of the connection destination candidatecells (adjacent cells) is present (ST304). Upon receiving the inquiry,the historical information manager 54 searches and (if found) acquiresthe requested historical obstruction information in the communicationhistory database stored in the storage 34.

If the historical obstruction information on any one of the connectiondestination candidate cells is present (Yes in ST304), the connectiondestination controller 56 calculates an offset based on an obstructedlocation included in the historical obstruction information for theconnection destination candidate cell, a moving velocity and a movingdirection of the user terminal, and then determines an obstructed area(ST305).

Next, the connection destination controller 56 determines whether or notthe user terminal is located within a risky area based on the currentlocation information of the user terminal (ST306). Then, the connectiondestination controller 56 calculates a distance from the currentlocation of the user terminal to the obstructed location, and determineswhether the distance is greater than the radius of the risky area (avalue obtained by adding the offset to a reference value).

If the user terminal is located within the risky area (Yes in ST306),the connection destination controller 56 selects connection destinationcandidates in such a manner as to avoid selecting a connectiondestination candidate(s) for which historical obstruction information ispresent (ST307).

If the user terminal is not located within the risky area (No in ST306),the connection destination controller 56 selects connection destinationcandidates so as not to exclude a connection destination candidate(s)for which historical obstruction information is present (ST308).

If the connection destination controller 56 does not perform videocommunication (No in ST301) or if the historical obstruction informationon any one of the connection destination candidate cells is not present(No in ST304), the connection destination controller 56 ends theoperation without any further processing.

It should be noted that, since a new connection destination isdetermined by a network side device such as the macro cell base station3, when excluding a particular cell(s) from connection destinationcandidates, the connection destination controller 56 only has to requestsuch a network side device to determine a new connection destination insuch a manner as to avoid connecting to the particular cell(s) to beexcluded. In this case, the connection destination controller 56 may beconfigured to, when transmitting a measurement report for reportingcommunication quality measurements, change a measurement result for eachcell to be excluded to a lower value than an actual measurement resultor to exclude cells to be excluded from cells for which the connectiondestination controller 56 is to report measurement results. The networkside device selects a cell providing the highest communication qualityas a connection destination, and thus excludes the cell(s) s to beexcluded from connection destination candidates because of its poorcommunication quality.

In the embodiments shown in FIGS. 9,10 and 11, the user terminalperforms the connection destination change operation and the connectiondestination candidate selection operation only while an application iscurrently performing video communication. In other embodiments, the userterminal may be configured to be capable of performing the operationswhile an application is not performing video communication.

Second Embodiment

Next, a second embodiment of the present invention will be described.Except for what will be discussed here, this embodiment is the same asthe above-described embodiment.

In the first embodiment, the user terminal 1 is configured to determinethe size of a risky area based on moving status (a moving velocity and amoving direction) of the user terminal 1, and then determine a degree ofrisk of occurrence of decrease in communication quality based on whetheror not the user terminal 1 is located within the risky area. However, inthe present embodiment, a user terminal 1 determines a degree of risk ofoccurrence of decrease in communication quality based on a time periodrequired for the user terminal to reach the obstructed location(accession time period).

Specifically, the user terminal calculates a distance from the currentlocation of the user terminal to the obstructed location. Then, the userterminal calculates an accession time period based on the calculateddistance and a moving velocity and a moving direction of the userterminal 1, and then determines whether or not the accession time periodis shorter than a predetermined threshold value. If the accession timeperiod is shorter than the predetermined threshold value, the userterminal 1 determines that there is a risk of occurrence of decrease incommunication quality.

For example, in cases where the distance from the current location ofthe user terminal to the obstructed location is 30 m and thepredetermined threshold value is 10 s, when a moving velocity is 4 km/h,the accession time period is 27 s, which is longer than the thresholdvalue of 10 s and thus the user terminal determines that there is not arisk of occurrence of decrease in communication quality. When a movingvelocity is 30 km/h, the accession time period is 3.6 s, which isshorter than the threshold value of 10 s and thus the user terminaldetermines that there is a risk of occurrence of decrease incommunication quality.

The user terminal 1 preferably calculates an accession time period basedon a velocity component in the direction from the current location ofthe user terminal 1 to an obstructed location in the same manner as thefirst embodiment.

In the first embodiment, the user terminal 1 is configured to determinethe size of a risky area based on moving status of the user terminal 1,a type of application currently performing communication, and/or a typeof the user terminal 1 in order to determine a degree of risk ofoccurrence of decrease in communication quality. The user terminal 1 inthe present embodiment may also be configured to determine a degree ofrisk of occurrence of decrease in communication quality based on movingstatus of the user terminal 1, a type of application currentlyperforming communication, and/or a type of the user terminal 1 in thesame manner as the first embodiment. In this case, the threshold valuemay be changed or the accession time period may be corrected based onmoving status of the user terminal 1, a type of application currentlyperforming communication, and/or a type of the user terminal 1.

Next, an operation procedure of the user terminal 1 according to thesecond embodiment will be described. FIG. 12 is a flowchart showing anoperation procedure of a connection destination change operationperformed by a user terminal 1. FIG. 13 is a flowchart showing anoperation procedure of a connection destination candidate selectionoperation.

As shown in FIG. 12, when performing the connection destination changeoperation, the connection destination controller 56 performs theprocessing operations from ST201 to ST204 in the same manner as thefirst embodiment (See FIG. 9).

If the historical obstruction information on the current connectiondestination is present (Yes in ST204), the connection destinationcontroller 56 calculates a distance from the current location of theuser terminal to the obstructed location based on historical obstructioninformation for a current connection destination and information on thecurrent location of the user terminal (ST211).

Next, the connection destination controller 56 calculates an accessiontime period based on the distance from the current location to theobstructed location, and a moving velocity and a moving direction of theuser terminal 1, and then determines whether or not the accession timeperiod is shorter than a predetermined threshold value (ST212).

If the accession time period is shorter than the predetermined thresholdvalue; that is, there is a risk of occurrence of decrease incommunication quality (Yes in ST212), the connection destinationcontroller 56 changes the connection destination (ST207).

If the accession time period is not shorter than the predeterminedthreshold value; that is, there is not a risk of occurrence of decreasein communication quality (No in ST212), the connection destinationcontroller 56 ends the operation without any further processing.

As shown in FIG. 13, when selecting connection destination candidates,the connection destination controller 56 performs the processingoperations from ST301 to ST304 in the same manner as the firstembodiment (See FIG. 10).

If the historical obstruction information on any one of the connectiondestination candidates is present (Yes in ST304), the connectiondestination controller 56 calculates a distance from the currentlocation of the user terminal to the obstructed location based onhistorical obstruction information for the connection destinationcandidate and information on the current location of the user terminal(ST311).

Next, the connection destination controller 56 calculates an accessiontime period based on the distance from the current location to theobstructed location and a moving velocity and a moving direction of theuser terminal 1, and then determines whether or not the accession timeperiod is shorter than a predetermined threshold value (ST312).

If the accession time period is shorter than the predetermined thresholdvalue; that is, there is a risk of occurrence of decrease incommunication quality (Yes in ST312), the connection destinationcontroller 56 selects connection destination candidates in such a manneras to avoid selecting a connection destination candidate(s) for whichhistorical obstruction information is present (ST307).

If the accession time period is not shorter than the predeterminedthreshold value; that is, there is not a risk of occurrence of decreasein communication quality (No in ST312), the connection destinationcontroller 56 selects connection destination candidates so as not toexclude a connection destination candidate(s) for which historicalobstruction information is present (ST308).

Third Embodiment

Next, a third embodiment of the present invention will be described.Except for what will be discussed here, this embodiment is the same asthe above-described embodiments. FIG. 14 is an explanatory view showingan outline of connection destination control operations performed by auser terminal 1 according to the third embodiment of the presentinvention.

In the above-described embodiments, the user terminal 1 is configured todetermine a degree of risk of occurrence of decrease in communicationquality and control a cell of as the connection destination. However, inthe present embodiment, a user terminal 1 controls a beam used as theconnection destination. The other control operations of the presentembodiment are the same as the above-described embodiments, which meansthat, in the present embodiment, a cell(s) in the above-describedembodiments is replaced with a beam(s).

For example, with regard to a change in its connection destination, theuser terminal determines a degree of risk of occurrence of decrease incommunication quality associated with a currently-connected beam, andwhen there is a risk of occurrence of decrease in communication qualityassociated with the currently-connected beam, the user terminal changesthe beam as the connection destination from the currently-connected beamto a different beam. This control enables the user terminal to changeits connection destination from the currently-connected beam to anothersafe beam which does not involve a risk of occurrence of decrease incommunication quality.

In an example shown in FIG. 14A, when the user terminal 1 has reached alocation close to the obstructed location associated with thecurrently-connected beam B1, the user terminal changes its connectiondestination from the currently-connected beam to the safe beam B2 whichdoes not involve a risk of occurrence of decrease in communicationquality.

Moreover, when the user terminal 1 reaches a boundary of acurrently-connected beam and then changes its connection destination toanother beam, the user terminal 1 determines a degree of risk ofoccurrence of decrease in communication quality by obstructionassociated with each beam which is a connection destination candidate(transition destination), and performs control operations such that theuser terminal excludes a beam(s), which involves a risk of occurrence ofdecrease in communication quality due to obstruction, from theconnection destination candidate(s).

In an example shown in FIG. 14B, when the user terminal 1 reaches aboundary of the currently-connected beam B1 and is located close to anobstructed location associated with the beam B2 adjacent to the beam B1,control operations are performed such that the user terminal excludesthe beam B2, which involves a risk of occurrence of decrease incommunication quality, from the connection destination candidate(s), andchanges its connection destination to the safe beam B3 which does notinvolve such a risk of occurrence of decrease in communication quality.

In the present embodiment, the storage 34 stores information registeredin the communication history database in the same manner as the firstembodiment (See FIG. 4). In the present embodiment, the informationregistered in the communication history database includes information oneach beam (such as beam ID) and other related information.

In the present embodiment, the user terminal performs beam control insuch a manner as to control a beam used as its connection destination.However, the user terminal may be configured to perform this beamcontrol in combination with the cell control in the previous embodimentsin combination.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described.Except for what will be discussed here, this embodiment is the same asthe above-described embodiments.

In the first embodiment, the user terminal 1 is configured to perform aconnection destination control such that, when the user terminal 1 comesclose to an obstructed location and into a risky state in which decreasein communication quality is expected to occur, the user terminal 1prospectively changes its connection destination to a different saferconnection destination. However, in the present embodiment, the userterminal 1 is configured such that, when the user terminal 1 comes intoa risky state in which rapid reduction in an amount of availablecommunication bandwidth is expected to occur, the user terminal 1 lowersa current transmission rate for communicating data to a propertransmission rate. Since the user terminal reduces an amount ofavailable communication bandwidth used for transmitting data in advanceof reduction in an actual amount of available communication bandwidth,this configuration can prevent a packet stay in the network afterreduction in an actual amount of available communication bandwidth,thereby keeping the video from stopping.

Moreover, in the present embodiment, the user terminal is configuredsuch that a transmission rate at each location acquired during pastcommunication is registered in the communication history database ashistorical communication information, and to acquire, based on thehistorical communication information, an expected transmission rate atan expected location at which the user terminal is expected to belocated after a lapse of a predetermined time period, and communicatesdata at the expected transmission rate.

Furthermore, in the present embodiment, the user terminal determines adegree of risk of occurrence of reduction in an amount of availablecommunication bandwidth beyond a tolerance limit, based on whether ornot a rate difference between a current transmission and an expectedtransmission rate is greater than a predetermined threshold value.

Next, a general configuration of a user terminal 1 according to thefourth embodiment of the present invention will be described. FIG. 15 isa block diagram showing a general configuration of the user terminal 1according to the fourth embodiment. FIG. 16 is an explanatory viewshowing an example of historical communication information registered ina communication history database according to the fourth embodiment.

The user terminal 1 includes a wireless communication device 31, alocation information acquisition device 32, a controller 33, and astorage 34 as in the first embodiment (See FIG. 4).

The storage 34 stores information registered in the communicationhistory database. Items of the historical communication information inthe communication history database (See FIG. 16) includes date, time,location, RAT, frequency, cell ID, beam identifier, moving direction,communication quality, rate of change in communication quality, greatestdifference in communication quality between the current location andnearby locations, and RLF determination result, and further includesapplication information (app information), transmission rate, number ofpacket loss, and RTT.

The controller 33 includes a wireless communication controller 61, anapplication controller 62, a terminal status acquirer 63, a historicalinformation registerer 64, a historical information acquirer 65, and atransmission rate controller 66.

The wireless communication controller 61 controls wireless communicationperformed by the wireless communication device 31, and selects a properconnection destination (macro cell base station 3, small cell basestations 4, wireless LAN access point 5) based on communication qualityinformation or other relevant information.

The application controller 62 performs an operation(s) required for eachapplication, and transmits and receives data to and from the server 2via the wireless communication device 31.

The terminal status acquirer 63 acquires location information on acurrent location at which the user terminal is currently located andinformation on current moving status (moving velocity and movingdirection) as terminal status information.

The historical information registerer 64 registers historicalcommunication information on past communication status in thecommunication history database stored in the storage 34, where thehistorical communication information includes location information foreach location in which communication was performed in the past, andother information on past communication status (such as connectiondestination, communication quality, and transmission rate).

In response to an inquiry transmitted from the transmission ratecontroller 66, the historical information acquirer 65 searches andacquires historical communication information for a specified location(expected location where the user terminal is expected to reach) in thecommunication history database stored in the storage 34. In some cases,the historical information acquirer 65 may be configured to acquirehistorical communication information on past communications involving acertain communication quality level or higher (a certain packet lossrate or higher, a certain transmission delay level or lower) selectedfrom historical communication information including the same applicationinformation for a specified location (expected location). The historicalinformation acquirer 65 may be configured such that, when finding two ormore pieces of the historical communication information meeting suchselection conditions, the historical information acquirer 65 selectivelyacquires a piece of historical communication information on the latestcommunication, or, alternatively, the historical information acquirer 65selectively acquires a piece of historical communication information ona communication with the highest transmission rate. The latter selectioncondition is suitable for transmitting security surveillance video data,for example. In other cases, the historical information acquirer 65 isconfigured to notify the transmission rate controller 66 of averagedhistorical communication information obtained by averaging data seta inthe historical communication information on past communications withrather high communication quality. This configuration is suitable fortransmitting entertainment content video data.

In addition, the historical information acquirer 65 is configured suchthat, when failing to find historical communication informationincluding any application information nor historical communicationinformation including application information for an applicationcurrently used by the user terminal for communication, the historicalinformation acquirer 65 acquires a piece of historical communicationinformation obtained by selecting historical communication informationon a communication with the highest transmission rate for the expectedlocation, and then generating communication information corresponding toa virtual communication with a transmission rate lower than the highesttransmission rate by a certain level.

The transmission rate controller 66 control a transmission rate forcommunicating data based on a current transmission rate and historicalcommunication information acquired by the historical informationacquirer 65. In the present embodiment, the user terminal determines adegree of risk of occurrence of rapid reduction in an amount ofavailable communication bandwidth beyond a tolerance limit associatedwith an expected location at which the user terminal is expected to belocated after a lapse of a predetermined time period, and thetransmission rate controller 66 control a transmission rate forcommunicating the data based on a result of determination of the degreeof risk.

More specifically, in the present embodiment, the historical informationacquirer 65 acquires an expected transmission rate at the expectedlocation based on the historical communication information, andcommunicates data at the expected transmission rate. Furthermore, thecontroller is configured to determine that there is a risk of occurrenceof rapid reduction in an amount of available communication bandwidthbeyond the tolerance limit when the expected transmission rate is lowerthan a current transmission rate by a rate difference which is greaterthan a predetermined threshold value.

Next, an operation procedure of the user terminal 1 according to thefourth embodiment will be described. FIG. 17 is a flowchart showing anoperation procedure of the user terminal 1. FIG. 18 is a sequencediagram showing an operation procedure of the user terminal 1.

First, the transmission rate controller 66 acquires location informationon a current location of the user terminal from the terminal statusacquirer 63 (ST401). The transmission rate controller 66 also acquires amoving velocity and a moving direction of the user terminal from theterminal status acquirer 63 (ST402). Then, the transmission ratecontroller 66 acquires application information on an applicationcurrently performing communication from the application controller 62(ST403).

Them, the terminal status acquirer 63 calculates an expected location atwhich the user terminal is expected to be located after a lapse of apredetermined time period based on the moving velocity and the movingdirection of the user terminal. For example, the terminal statusacquirer 63 calculates an expected location at which the user terminalis expected to be located in the predetermined time period (For example,10 s)(ST404).

Next, the transmission rate controller 66 transmits an inquiry to thehistorical information acquirer 65 to check whether or not there ishistorical communication information for the expected location (ST405).In response, the historical information acquirer 65 searches forhistorical communication information including the same applicationinformation for the expected location in the communication historydatabase stored in the storage 34, and if found, acquires the historicalcommunication information.

If there is such historical communication information for the expectedlocation (Yes in ST405), the transmission rate controller 66 acquires atransmission rate included in the historical communication informationas an expected transmission rate at the expected location (ST406).

Next, the transmission rate controller 66 determines whether or not theexpected transmission rate is lower than a current transmission rate bya rate difference which is greater than a predetermined threshold value(ST407).

If the expected transmission rate is lower than the current transmissionrate by a rate difference which is greater than the predeterminedthreshold value (Yes in ST407), the transmission rate controller 66notifies the application controller 62 of the expected transmissionrate, whereby the application controller 62 adjusts the transmissionrate used for transmitting data (video data) to the expectedtransmission rate (ST408).

If there is no historical communication information for the expectedlocation (No in ST405) and/or if the expected transmission rate is lowerthan the current transmission rate by a rate difference which is notgreater than the predetermined threshold value (No in ST407), thetransmission rate controller 66 ends the operation without any furtherprocessing as there is not a risk of occurrence of reduction in anamount of available communication bandwidth beyond a tolerance limit. Ifthe expected transmission rate is greater than the current transmissionrate, it is preferable that the current transmission rate continues tobe used because, when the transmission rate is increased in advance, arequired communication bandwidth can exceed a current actual amount ofavailable communication bandwidth.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described.Except for what will be discussed here, this embodiment is the same asthe above-described embodiments.

In the fourth embodiment, the user terminal is configured such that atransmission rate for each location acquired during past communicationis registered in the communication history database as historicalcommunication information, and to acquire, based on the historicalcommunication information, an expected transmission rate at an expectedlocation at which the user terminal is expected to be located after alapse of a predetermined time period, and communicates data at theexpected transmission rate. However, in the present embodiment, a userterminal 1 is configured such that a connection destination for eachlocation is registered in the communication history database ashistorical communication information, and to acquire, based on thehistorical communication information, a connection destination at theexpected location, and communicates data at a transmission rate for theconnection destination.

Furthermore, in the fourth embodiment, the user terminal is configuredto determine a degree of risk of occurrence of reduction in an amount ofavailable communication bandwidth beyond a tolerance limit, based onwhether or not a rate difference between a current transmission and anexpected transmission rate is greater than a predetermined thresholdvalue. However, in the present embodiment, the user terminal isconfigured to determine the degree of risk based on whether or not atransmission capacity of an expected connection destination at theexpected location is lower than that of a current connectiondestination. For example, in a case where the connection destination ischanged from a 5G cell having a large transmission capacity of about 20Gbps to an LTE cell having a small transmission capacity of about 300Mbps, when both the cells are used by 100 users for communication, anamount of available communication bandwidth for each user is reducedfrom 200 Mbps in the 5G cell to 3 Mbps. In this way, in cases where anexpected connection destination has a lower communication capacity thana current connection destination, a risk that the expected connectiondestination cannot accommodate the communication bandwidth currentlyused for communication, resulting in occurrence of a packet stay in thenetwork, which leads to decrease in quality of video.

In the present embodiment, the storage 34 of the user terminal 1 storesinformation registered in a communication history database in the samemanner as the fourth embodiment (See FIGS. 15 and 16). In the presentembodiment, the information registered in the communication historydatabase includes a connection destination for each location. Thestorage 34 also stores a transmission rate table (FIG. 19).

The transmission rate table according to a fifth embodiment of thepresent invention will be described. FIG. 19 is an explanatory viewshowing an example of the transmission rate table.

The transmission rate controller 66 of the user terminal 1 acquires aconnection destination for an expected location at which the userterminal 1 is expected to be located in a certain time period, andcommunicates data with the connection destination at a transmission ratecorresponding thereto. In the present embodiment, the transmission ratecontroller 66 acquires such a transmission rate for a connectiondestination for an expected location based on the transmission ratetable (preset transmission rate information) stored in the storage 34.

Information registered in the transmission rate table includestransmission rates each for a corresponding RAT (Radio AccessTechnology) of a connection destination. In the example of FIG. 19, thetable includes respective transmission rates for RATs; that is, LTE(Long Term Evolution), 802.11ac, and 802.11n (802.11ac and 802.11n arestandards for wireless LANs established by IEEE. The Institute ofElectrical and Electronics Engineers).

Next, an operation procedure of the user terminal 1 according to thefifth embodiment of the present invention will be described. FIG. 20 isa flowchart showing an operation procedure of the user terminal 1according to the fifth embodiment.

The transmission rate controller 66 performs the processing operationsfrom ST401 to STG105 in the same manner as the fourth embodiment (SeeFIG. 17). When the historical communication information does not includeany application information nor application information for anapplication currently used by the user terminal 1 for communication, thehistorical information acquirer can acquire historical communicationinformation for an expected location.

If there is such historical communication information for the expectedlocation (Yes in ST405), the transmission rate controller 66 acquires aconnection destination included in the historical communicationinformation as an expected connection destination for the expectedlocation (ST411).

Next, the transmission rate controller 66 compares a communicationcapacity of the expected connection destination with that of the currentconnection destination to thereby determine whether or not thecommunication capacity of the expected connection destination is lowerthan that of the current connection destination (ST412).

If the communication capacity of the expected connection destination islower than that of the current connection destination (Yes in ST412),the transmission rate controller 66 acquires a transmission rate for theexpected connection destination based on the transmission rate table asan expected transmission rate (ST413).

Next, the transmission rate controller 66 notifies the applicationcontroller 62 of the expected transmission rate, whereby the applicationcontroller 62 adjusts the transmission rate used for transmitting data(video data) to the expected transmission rate (ST408).

If there is no historical communication information for the expectedlocation (No in ST405) and/or if the communication capacity of theexpected connection destination is not lower than that of the currentconnection destination (No in ST412), the transmission rate controller66 ends the operation without any further processing. If thecommunication capacity of the expected connection destination is greaterthan that of the current connection destination, it is preferable thatthe current transmission rate continues to be used because, when thetransmission rate is increased in advance, a required communicationbandwidth can exceed a current actual amount of available communicationbandwidth.

While specific embodiments of the present invention are described hereinfor illustrative purposes, the present invention is not limited thereto.It will be understood that various changes, substitutions, additions,and omissions may be made for elements of the embodiments withoutdeparting from the scope of the invention. In addition, elements andfeatures of the different embodiments may be combined with each other asappropriate to yield an embodiment which is within the scope of thepresent invention.

For example, in the above-described embodiments, a user terminal isconfigured to accumulate historical obstruction information therefor andcontrol a connection destination based on the historical obstructioninformation, or configured to accumulate historical communicationinformation therefor and control a transmission rate based on thehistorical communication information. However, in other embodiments, auser terminal may be configured to upload historical obstructioninformation thereto and/or historical communication information thereonto a communication control device in the network, so that the userterminal can share the uploaded information with other user terminalsvia the network.

In addition, in the above-described embodiments, a user terminal isconfigured such that each user terminal itself performs controloperations (such as determination of a degree of risk, selection of aconnection destination and selection of a transmission rate) based onhistorical obstruction information and/or historical communicationinformation. However, a communication control device in the network maybe configured to perform all or part of the necessary control operationsbased on historical obstruction information and/or historicalcommunication information uploaded thereto.

INDUSTRIAL APPLICABILITY

A communication device, a communication system, a connection destinationcontrol method, and a transmission rate control method according to thepresent invention achieve an effect of allowing for prospectiveavoidance of decrease in communication quality due to obstruction and/orrapid reduction in an amount of available communication bandwidth,thereby enabling users to avoid encountering significant reduction inQuality of Experience, and are useful as a communication device forcommunicating data via a base station used as a connection destination,a communication system in which a communication device communicates datavia a base station used as a connection destination, a connectiondestination control method for controlling a connection destination fora communication device to communicate data via a base station used asthe connection destination, and a transmission rate control method forcontrolling a transmission rate at which a communication devicecommunicates data via a base station used as a connection destination.

Glossary

-   1 user terminal (communication device)-   2 server-   3 macro cell base station (base station device)-   4 small cell base station (base station device)-   5 access point (base station device)-   31 wireless communication device-   32 location information acquisition device-   33 controller-   34 storage

The invention claimed is:
 1. A communication device for communicatingdata via a base station used as a connection destination, thecommunication device comprising: a wireless communication deviceconfigured to wirelessly communicate with the base station used as theconnection destination; a location information acquisition deviceconfigured to acquire location information on a location of thecommunication device; a storage configured to store historicalcommunication information on past communication status; and a controllerconfigured to: determine a degree of risk of occurrence of reduction inan amount of available communication bandwidth beyond a tolerance limitbased on the historical communication information and the locationinformation, the degree of risk being determined for an expectedlocation at which the communication device is expected to be locatedafter a lapse of a predetermined time period; and control a transmissionrate for communicating the data based on a result of determination ofthe degree of risk.
 2. The communication device according to claim 1,wherein the storage configured to store a transmission rate andapplication information both for each location as historicalcommunication information, and wherein the controller is configured to,based on the historical communication information, acquire applicationinformation on an application currently performing communication and anexpected transmission rate at the expected location, and communicatesthe data at the expected transmission rate.
 3. The communication deviceaccording to claim 2, wherein the controller is configured to determinethat there is a risk of occurrence of decrease in communication qualitydue to obstruction when the expected transmission rate is lower than acurrent transmission rate by a rate difference which is greater than apredetermined threshold value.
 4. The communication device according toclaim 1, wherein the storage configured to store a connectiondestination for each location as historical communication information,and wherein the controller is configured to, based on the historicalcommunication information, acquire an expected connection destination atthe expected location, and communicate the data at a transmission ratefor the expected connection destination.
 5. The communication deviceaccording to claim 4, wherein the controller is configured to determinethat there is a risk of occurrence of decrease in communication qualitydue to obstruction when a transmission capacity of the expectedconnection destination at the expected location is lower than that of acurrent connection destination.
 6. A communication system in which acommunication device communicates data via a base station used as aconnection destination, wherein the communication device comprises: awireless communication device configured to wirelessly communicate withthe base station used as the connection destination; a locationinformation acquisition device configured to acquire locationinformation on a location of the communication device; a storageconfigured to store historical communication information on pastcommunication status; and a controller configured to: determine a degreeof risk of occurrence of reduction in an amount of availablecommunication bandwidth beyond a tolerance limit based on the historicalcommunication information and the location information, the degree ofrisk being determined for an expected location at which thecommunication device is expected to be located after a lapse of apredetermined time period; and control a transmission rate forcommunicating the data based on a result of determination of the degreeof risk.
 7. A transmission rate control method for controlling atransmission rate at which a communication device communicates data viaa base station used as a connection destination, the method comprising:the communication device determine a degree of risk of occurrence ofreduction in an amount of available communication bandwidth beyond atolerance limit based on historical communication information on pastcommunication status and location information on a location of thecommunication device, the degree of risk being determined for anexpected location at which the communication device is expected to belocated after a lapse of a predetermined time period; and thecommunication device controlling a transmission rate for communicatingthe data based on a result of determination of the degree of risk.